The present invention relates generally to medical devices and particularly to a stent with a graft retained against the stent.
Although stent graft assemblies may be used to treat a number of medical conditions, one common use of stent graft assemblies relates to the treatment of aneurysms. As those in the art well know, an aneurysm is an abnormal widening or ballooning of a portion of an artery. Generally, this condition is caused by a weakness in the blood vessel wall. High blood pressure and atherosclerotic disease may also contribute to the formation of aneurysms. Aneurysms may form in blood vessels throughout the vasculature. However, common types of aneurysms include aortic aneurysms, cerebral aneurysms, popliteal artery aneurysms, mesenteric artery aneurysms, and splenic artery aneurysms. If not treated, an aneurysm may eventually rupture, resulting in internal hemorrhaging. In many cases, the internal bleeding is so massive that a patient can die within minutes of an aneurysm rupture. For example, in the case of aortic aneurysms, the survival rate after a rupture can be as low as 20%.
Traditionally, aneurysms have been treated with surgery. For example, in the case of an abdominal aortic aneurysm, the abdomen is opened surgically and the widened section of the aorta is removed. The remaining ends of the aorta are then surgically reconnected. In certain situations the surgeon may choose to replace the excised section of the aorta with a graft material such as Dacron, instead of directly reconnecting the two ends of the blood vessel together. In still other situations, the surgeon may put a clip on the blood vessel at the neck of the aneurysm between the aneurysm and the primary passageway of the vessel. The clip then prevents blood flow from the vessel from entering the aneurysm.
An alternative to traditional surgery is endovascular treatment of the blood vessel with a stent-graft. This alternative involves implanting a stent-graft in the blood vessel across the aneurysm using conventional catheter-based based placement techniques. The stent-graft treats the aneurysm by sealing the wall of the blood vessel with an impermeable graft material. Thus, the aneurysm is sealed off and the blood flow is kept within the primary passageway of the blood vessel. Increasingly, treatments using stent-grafts are becoming preferred since the procedure results in less trauma and a faster recuperation.
Although stent-grafts are mostly used for treating aneurysms, other medical treatments using stent-grafts are also being explored, and additional applications may be developed in the future. For example, stent-grafts may be used to treat stenosed arteries or other vascular conditions. Stent-grafts may also be used to treat other non-vascular organs, such as the biliary tract. In yet another example, other types of graft materials may be used besides the conventional graft materials that are usually used for aneurysm treatments. While the graft materials that are used for aneurysm treatments are designed to block fluid passage through the graft material, other types of graft materials may be used in stent-grafts, such as small intestine submucosa (“SIS”). As those in the art know, SIS has growth factors that encourage cell migration within the graft material, which eventually results in the migrated cells replacing the graft material with organized tissue.
One current problem with stent-grafts is the way in which the graft material is attached to the stent. The most common way of attaching graft material to a stent is to sew, or suture, the graft material to the stent with thread. However, this process must be done manually by specialists who use special needles to sew thread through the graft material and around the struts of the stent and forceps to knot the thread. As a result, stent-grafts made by this process are expensive and time consuming to make.
In addition, stent-grafts that are made by suturing may suffer from endoleaks once the stent-graft is implanted across an aneurysm. As those in the art know, an endoleak is a blood flow leakage from the lumen of the blood vessel back into the aneurysm. A large amount of leakage after implantation of the stent-graft reduces the effectiveness of the treatment and may leave the patient with a continued risk of rupture despite the treatment. One common source of endoleaks is the perforations through the graft material which are generated by the suturing used to attach the graft material to the stent. In an attempt to overcome the problem of endoleaks, manufacturers of stent-grafts have turned to using especially small diameter needles and thread for the suturing process in order to minimize the size of the perforations. However, this does not completely eliminate the perforations through the graft material and endoleaks through the graft material are still possible. Moreover, this solution increases the cost of stent-grafts even further, since small diameter needles and threads are difficult to work with manually and even require the use of magnifying glasses in some situations.
Another way of attaching graft material to a stent is to sandwich the graft material between an inner stent and an outer stent. In this type of arrangement, opposing pressure from the inner and outer stents squeezes the graft material therebetween. If enough pressure is applied to the graft material by the two stents, the graft material will become immobilized between the stents. However, the known stent-grafts which attempt to sandwich graft material between two stents do not have complimentary features on both stents which cooperate to secure the graft material. Moreover, the known stent-grafts do not orient the two stents together so that cooperative features can secure the stent graft.
Accordingly, it is apparent to the inventor that a stent-graft is desired with cooperative features that secure a graft material to a stent without perforating the graft material. Therefore, a solution is described more fully below that solves these and other problems.